1. Field of the Invention
The present invention generally relates to a magnetoresistive device having a magnetoresistive element (MR element) and, more particularly, to a thin-film magnetoresistive device having an MR element through which a current flows in a direction perpendicular to a plane of the MR element.
2. Description of the Related Art
FIG. 1 is an illustration of a conventional magnetic reproducing head formed as a thin-film device having an MR element, viewed from a side of a magnetic recording medium from which information is read by the magnetic reproducing head. In FIG. 1, a side-to-side direction corresponds to the direction of width of a track formed on the magnetic recording medium.
The magnetic reproducing head shown in
FIG. 1 comprises an MR element 100, an upper shielding layer 101, a lower shielding layer 102, an upper gap layer 103 and a lower gap layer 104. The MR element 100 is interposed between the lower gap layer 104 and the upper gap layer 103. The upper shielding layer 101 is formed on a surface of the upper gap layer 103 which surface is opposite to the MR element 100, and the lower shielding layer 102 is formed on a surface of the lower gap layer 104 which surface is opposite to the MR element 100. Each of the upper shielding layer 101 and the lower shielding layers 102 is formed from a soft magnetic material such as NiFe. Each of the upper gap layer 103 and the lower gap layer 104 is formed from an insulating material such as alumina (aluminum oxide).
Additionally, lead wires 105A and 105B are provided on the left side and the right side of the MR element 100, respectively, so as to electrically detect a change in a magnetoresistance of the MR element 100. Further, hard magnet layers 106A and 106B are formed between the lower gap layer 104 and each of the lead wires 105A and 105B, respectively. Each of the hard magnet layers 106A and 106B is formed from a material such as CoPt which has hard magnetic properties so as to eliminate a Balkhausen noise.
In the above-mentioned magnetic reproducing head, a change in the magnetoresistance of the MR element 100 can be sensed as a change in a voltage across the MR element 100 by providing a current flowing between the lead wires 105A and 105B connected to the MR element 100. Accordingly, when the magnetic reproducing head (magnetoresistive device) is positioned close to a magnetic recording medium such as a hard disk, a change occurs in the magnetoresistance of the MR element 100 in the magnetoresistive device due to a change in an electric field generated by the magnetic recording medium. Thus, such a change in the magnetoresistance can be sensed as a change in the voltage across the MR element 100.
It should be noted that the magnetic reproducing head shown in FIG. 1 is referred to as a current-in-plane (CIP) type thin-film magnetic head since a current flows from the lead wire 105A to the lead wire 105B along a plane of the MR element 100.
Japanese Laid-Open Patent Application No.9-288807 discloses another thin-film magnetic head as shown in FIG. 2. This thin-film magnetic head has a structure different from that of the thin-film head shown in FIG. 1, and is referred to as a current perpendicular (CPP) type thin-film magnetic head in which a current flows in a direction perpendicular to a plane of the MR element. That is, a current flows in a longitudinal direction in FIG. 2.
The thin-film magnetic head shown in FIG. 2 comprises an MR element 110, an upper shielding layer 111, a lower shielding layer 112, an upper gap layer 113 and a lower gap layer 114. The MR element 110 is interposed between the lower gap layer 114 and the upper gap layer 113. The upper shielding layer 111 is formed on a surface of the upper gap layer 113 which surface is opposite to the MR element 110, and the lower shielding layer 112 is formed on a surface of the lower gap layer 114 which surface is opposite to the MR element 110. Each of the upper shielding layer 111 and the lower shielding layers 112 is formed of a metallic, magnetic material having good conductivity. Each of the upper gap layer 113 and the lower gap layer 114 is formed from a conductive material such as Cu. Additionally, insulating layers 117A and 117B are provided on the left side and right side of the MR element 110, respectively, so as to fill a gap between the lower shielding layer 112 and the upper shielding layer 111. Each of the insulating layers 117A and 117B is formed from an insulating material such as alumina.
In the thin-film magnetic head shown in FIG. 2, a current flows from the upper shielding layer 111 to the upper gap layer 113, traverses the MR element 110 and finally reaches the lower shielding layer 112 via the lower gap layer 114.
In recent years, density of data recorded on a recording medium is greatly increased. In order to read the high-density data on the recording medium, a gap of the device must be reduced. Accordingly, in the conventional magnetic reproducing head shown in FIG. 1, a thickness of each of the upper and lower gap layers 103 and 104 has been reduced. However, in order to maintain sufficient insulation, the thickness of each of the upper and lower gap layers 103 and 104 must be maintained to be about 30 nm, and it is difficult to further reduce the gap.
The thin-film magnetic head shown in FIG. 1 is the CIP type in which a current flows along a plane of the MR element. Recently, a giant magnetoresistive (GMR) element has been developed. It is found that the sensitivity of the GMR element of a spin valve type can be increased by providing a current to flow in a direction perpendicular to the plane of the GMR element. However, such an attempt cannot be made to the thin-film magnetic head shown in FIG. 1 since the thin-film magnetic head shown in FIG. 1 is of the CIP type. Additionally, a tunnel type GMR element requires a current flowing in a direction perpendicular to a plane of the GMR element, and, thus, the tunnel type GMR element cannot be used in the thin-film magnetic head shown in FIG. 1.
In the CPP type thin-film magnetic head shown in FIG. 2, the gap between the shielding layers is reduced further than the CIP type thin-film magnetic head. Additionally, the CPP type thin-film magnetic head shown in FIG. 2 has a structure in which a current flows in a direction perpendicular to a plane of the MR element. However, the thin-film magnetic head shown in FIG. 2 does not satisfy the requirement to use the MR element by efficiently supplying a current in a direction perpendicular to a plane of the MR element. Additionally, the thin-film device has a problem in that a free layer of the MR element may be deteriorated by an underlayer material.
It appears that a Balkhausen noise can be reduced by applying the hard magnet layer of the thin-film device shown in FIG. 1 to the thin-film device shown in FIG. 2. However, the structure of the hard magnetic layer shown in FIG. 1 has a problem in that a yield rate is decreased due to a short-circuit between the MR element and the upper gap layer. Thus, mere application of the hard magnetic layer to the thin-film device shown in FIG. 2 cannot provide a preferred effect.